Obesity is a serious, chronic disease that can harm a person’s health. A person is generally considered obese if he or she has a body mass index (BMI) greater than 30. Public health professionals agree that overweight and obesity have reached epidemic proportions in the U.S. According to a recent national survey, one out of five or 17 percent of U.S. children, ages 6 to 19, are overweight or obese. In addition, more than one third of the U.S. population is overweight or obese—35 percent of women and 33 percent of men. Overweight and obesity together represent the second leading preventable cause of death in the U.S. Overweight and obesity are not the same; rather, they are different points on a continuum of weight ranging from being underweight to being morbidly obese. The percentage of people who fit into these two categories, overweight and obese, is determined by BMI. BMI is a measure of weight proportionate to height. BMI is considered a useful measurement of the amount of body fat. Occasionally, some very muscular people may have a BMI in the overweight range. However, these people are not considered overweight because muscle tissue weighs more than fat tissue. Generally, BMI can be considered an effective way to evaluate whether a person is overweight or obese. In adults, a BMI from 18.5 to 24.9 is considered normal while a BMI of more than 25 is considered overweight. A person is considered obese if the BMI is greater than 30 and morbidly obese if the BMI is 40 or greater. When assessing a child's weight, the BMI is calculated and then plotted on a BMI for age percentile curve. Another measure of obesity is the waist-to-hip ratio (WHR). The WHR is a measurement tool that looks at the proportion of fat stored on the waist, and hips and buttocks. The waist circumference indicates abdominal fat. A waist circumference more than 40 inches in men and more than 35 inches in women may increase the risk for heart disease and other diseases associated with being overweight. In many ways, obesity is a puzzling disease. How the body regulates weight and body fat is not well understood. On one hand, the cause appears to be simple in that if a person consumes more calories than he or she expends as energy, then he or she will gain weight. However, the risk factors that determine obesity can be a complex combination of genetics, socioeconomic factors, metabolic factors, and lifestyle choices. Some endocrine disorders, diseases, and medications may also exert a powerful influence on an individual's weight. Studies have shown that a predisposition toward obesity can be inherited. Although researchers have identified several genes that appear to be associated with obesity, most believe that one gene is not responsible for the entire obesity epidemic. There is a strong relationship between economic status and obesity, especially among women. Women who are poor and of lower social status are more likely to be obese than women of higher socioeconomic status. The occurrence of obesity is also highest among minority groups, especially among women. Overeating, along with a sedentary lifestyle, contributes to obesity. These are lifestyle choices that can be affected by behavior change. Eating a diet in which a high percentage of calories come from sugary, high-fat, refined foods promotes weight gain. Lack of regular exercise contributes to obesity in adults and makes it difficult to maintain weight loss. In children, inactivity, such as watching television, playing too many video games, or sitting at a computer, contributes to obesity. Obesity has a far-ranging negative effect on health. The health effects associated with obesity include high blood pressure, diabetes, heart disease, joint problems like osteoarthritis, sleep apnea and respiratory problems, cancer, and metabolic syndrome.